A1
は — what the sentence is about
How the Japanese topic particle は works, why it is read “wa” rather than “ha”, and why “the topic” is not the same thing as “the subject”.
は marks what the sentence is about. Everything after it is the comment on that topic.
私は学生です。
Watashi wa gakusei desu.
I’m a student.
今日は寒いです。
Kyō wa samui desu.
It’s cold today.
It is written は and said wa. The character is the hiragana ha, and as a particle it keeps the old spelling and takes the modern sound. This catches every beginner once and never again.
Topic, not subject
English has no topic marker, so the distinction takes a while. は does not say who did it — it says what we are talking about, and the rest of the sentence can be about something else entirely.
象は鼻が長いです。
Zō wa hana ga nagai desu.
Elephants have long noses.
Read literally that is as for elephants, the nose is long. 象 is the topic, 鼻 is the subject of 長い. English has to restructure the whole sentence; Japanese puts one particle after each and leaves the rest alone.
It replaces other particles
は does not stack with が or を. When the thing you want as topic would otherwise be marked by one of those, は takes its place.
寿司は食べません。
Sushi wa tabemasen.
I don’t eat sushi.
寿司 is the object — it would take を — but marking it as topic replaces that.
寿司をは食べません。
寿司は食べません。
を and は cannot both mark 寿司. は displaces it. The particles that do stack with は are に and で: 学校では, at school, as for that.
Contrast
は carries a hint of comparison with something unsaid, which is why the two sentences below feel different.
コーヒーは好きです。
Kōhī wa suki desu.
I like coffee.
That can quietly imply …tea, less so. It is one reason a beginner’s Japanese sometimes lands oddly: は on a plain statement can sound like the first half of a contrast you never made.